My goal is to pass a Scala file created by my app Wilsonic to Thumbjam as efficiently as possible, with as few user-initiated steps as possible.

For iOS devices 9.x+: When Wilsonic creates a NSURL to a sandboxed Scala file, and passes that to UIActivityViewController: Thumbjam does not show up as an option.

When I take the same NSURL and use MFMailComposeViewController to attach the data as type "application/wilsonic" with a .scl suffix: Mail's presentation of UIActivityController includes Thumbjam. Which is very efficient except for the step of having to email Scala files to oneself.

There is something that iOS Mail client is doing that understands that this Scala file can be opened by Thumbjam, that my app is not doing.

What can my iOS app do to share files that Thumbjam will always recognize as Scala files?